The overall goal of the invention is to enhance independent walking function in people with incomplete spinal cord injury (SCI), post stroke, and other similar injuries or conditions by minimizing the amount of walking assistance provided or by adding targeted resistance to the legs during body weight supported treadmill training (BWSTT). Providing targeted resistance load based on the motor performance of the patient improves the training outcomes of BWSTT through enhanced patient effort that effectively engages adaptive sensorimotor processes.
Spinal Cord Injury
The estimated prevalence of SCI in the United State is approximately 253,000 individuals. Approximately 52% of the people with SCI suffer from functionally incomplete spinal cord injury and could benefit from gait retraining. With the emergence of new treatments such as cell implants, the use of growth-stimulating factors and other technologies, the number of people with SCI needing gait retraining is likely to increase even further.
One of the most common goals of patients with SCI is regaining walking ability, as limitations in mobility can affect most activities of daily living. Following an SCI, descending spinal pathways are damaged. The loss of descending input to spinal neurons may reduce synaptic drive to locomotor networks and also compromise the ability to produce voluntary movements of the limbs. As a result, an obvious consequence of SCI is paralysis, or weakness of lower extremity muscles that may have a substantial adverse impact on walking.
Individuals with SCI may suffer difficulties supporting their body weight during the stance phase of gait or lifting and bringing the leg forward during swing due to the muscular weakness associated with the injury. As a consequence, people with SCI often require assistive devices, such as a rolling walker, and spend more of the gait cycle in double support (i.e., bearing weight in both legs to improve support).
In general, successful locomotor recovery following SCI depends on the availability of residual descending commands and on maximizing neural plasticity of spinal and supraspinal locomotor networks. The neural reorganization achieved during rehabilitation is highly dependent on the magnitude and specificity of targeted neural activity. Thus, to maximize motor recovery, the various embodiments of the present invention offer rehabilitation after neurological injury that emphasizes active, repetitive, task-specific practice that maximizes neuromuscular activity.
Current BWSTT techniques are generally designed to improve motor function and ambulation in people with SCI. During such current BWSTT, the patient is given body weight support and assisted to move their legs in a “kinematically correct gait” by a physical therapist. This training paradigm largely meets criteria for effective neuroplasticity: the training is task-specific and utilizes both active and sensory pathways of the relevant neuromuscular systems.
Stroke
Stroke is currently the leading cause of disability in the U.S. with approximately 1.1 million individuals currently with stroke-related disabilities. Impaired mobility is an important factor in determining the degree of physical disability after stroke. While up to 80% of individuals with stroke may ultimately recover the ability to walk short distance, most of them do not achieve the locomotor capacity necessary for community ambulation. Walking ability post-stroke is characterized primarily by reduced walking speed and endurance, residual spatial and temporal left-right asymmetry, and impaired postural stability. Patients post-stroke suffer a greatly reduced knee flexion at toe off and peak knee flexion during swing of the paralyzed leg compared to the intact leg, which is usually associated with compensation by pelvic hiking and limb circumduction. The impaired hip and knee flexion during swing phase may result in a decreased forward progression and velocity, shortened step length and toe drag at initial swing. These impairments restrict independent mobility and severely impact post-stroke patients' quality of life.
Decreased overground walking speed is a result of decreased cadence, decreased stride length and increased non-paretic single limb stance duration. Mechanisms underlying reduced gait velocity are thought to be the weakness of the paretic limb, particularly hip flexor and plantarflexor strength, spasticity, and the loss of inter- and intra-limb coordination. Rehabilitation efforts to improve strength and muscle coordination patterns during hemiparetic gait may improve gait velocity and quality and therefore improve performance of activities of daily living.
To improve gait performance and functional outcomes following neurological injury, rehabilitation efforts have been focused on re-establishing normal walking patterns. Towards this end, the use of BWSTT has demonstrated significant improvement in walking capability in individuals post-stroke. By providing a portion of body weight over a treadmill and manual facilitation from therapists, research has demonstrated improvements in temporal-spatial gait patterns, including gait velocity, endurance, balance, and symmetry.
While statistically significant improvements in walking recovery with BWSTT have been shown, it remains unclear whether therapeutic effects of such training are maximized. Specifically, in studies that have employed high intensity walking regimens in individuals with chronic stroke (i.e., those without presumed spontaneous recovery), the average increase in walking speed ranges have been achieved. These increases equating to an increase of approximately 10% of healthy adult walking speed are small relative to the effort required to perform such training. In addition, the major limitation of BWSTT is that it requires greater involvement of the physical therapist, i.e., generally two or even more therapists are required in setting the paretic limb and controlling the trunk movement, and it is a labor intensive work for physical therapists, particularly for those patients who require substantial walking assistance following stroke. As a consequence, there is a need to produce greater functional improvements in a larger patient population.
Current Robotic Systems
Due to these limitations in BWSTT, several robotic systems have been developed for automating locomotor training, such as the Lokomat gait trainer (Colombo et al. “Treadmill Training of Paraplegic Patients Using a Robotic Orthosis,” J. Rehabil Res. Dev. 37:693-700 (2000)) and the Gait Trainer (GT) (Hesse et al. “A Mechanized Gait Trainer for Restoration of Gait,” J. Rehabil Res. Dev. 37:701-708 (2000)). The Lokomat gait trainer is a motorized exoskeleton that drives hip and knee motion with a fixed trajectory using four DC motors, but it is difficult to back drive the Lokomat because it uses high-advantage, ball screw actuators. The Gait Trainers rigidly drive the patient's feet through a stepping motion using a crank-and-rocker mechanism attached to foot platforms. These robotic systems had at their onset the basic design goal of firmly assisting patients in producing correctly shaped and timed locomotor movements.
This approach is effective in reducing therapist labor in locomotor training and increasing the total duration of training but shows relatively limited functional gains for some patients. For instance, in tests, only 0.06 m/s gait speed improvement was obtained following 4 weeks of training using a Lokomat. Especially, recent data indicate that robotic-assisted BWSTT is even less effective in improving walking ability in individuals post stroke than physical therapist-assisted locomotor training. Such results suggest that currently available robotic-assisted BWSTT does not significantly help stroke patients or individuals with SCI regain gait function so that their principal benefit is in reducing the labor effort of the physical therapist.
The limited effectiveness of current robotic systems for locomotor training may be due to the employment of the fixed trajectory control strategy. The algorithms that have been used in current available robotic systems for locomotor training have focused primarily on repeated movements of the limbs via predefined, fixed-kinematic trajectories, although new control algorithms have been tested recently (Riener et al. “Patient-Cooperative Strategies for Robot-Aided Treadmill Training: First Experimental Results,” IEEE Trans Neural Syst. Rehabil. Eng., 13:380-94 (2005)).
This type of training, however, eliminates cycle-to-cycle variation in the kinematics of the leg, a fundamental feature of the natural neural control of repetitive movements such as stepping. Indeed, fixed kinematic trajectory may lead to a learned helplessness condition, in which patients have less self-controlled success in generating the appropriate stepping movement of the lower limbs. In addition, a robotic orthosis driven in a fixed pattern effectively limits the degrees of freedom of the leg motion as compared with naturally occurring muscle activation patterns.
In contrast, the present inventors have determined that motor learning is more effective with a robotic algorithm that allows some variability in the stepping pattern than with a fixed trajectory paradigm. Thus, a training algorithm that permits the intrinsic variability in the activation of motor pools may allow the spinal circuits to explore multiple patterns of activation and thereby optimize training effectiveness. Thus, the system of the present invention does not precisely control the trajectory of the leg, but rather allows patients freedom to volitionally move their legs during treadmill walking using a novel cable robotic system.
The resulting variations from step to step are believed to be an important feature in motor learning in accordance with the present invention. There are many examples of tasks having some intrinsic level of variation in both the biomechanics and the timing of the neurons recorded during the repetitive performance of the task. Stepping is an excellent example of a motor task that is performed routinely and repetitively, but even under the most controlled conditions on a treadmill, no two steps are identical. This intrinsic variation in stepping is highly suggestive of a fundamental feature of the neural control of movement. It is already known that complete and stereologically constant assistance reduces the level of activation of the motor circuits that generate stepping. Thus, the system does not control the kinematics of the lower limbs during stepping in a manner that produces minimal variation—a minimal variation results in poorer stepping ability than if some level of variation is allowed during the stepping.
Rather, variation in stepping can be retained during treadmill stepping by applying assistance as needed (AAN). An experienced therapist may guide the patient to achieve a targeted motion trajectory, giving help only when the patient exhibits a large deviation from some desired trajectory or has difficulty in performing the movement. By applying AAN, the efficacy of BWSTT is improved by increasing patient effort and active involvement in motor learning.
This is supported by observations that active motor training is more effective than passive training in eliciting performance improvement. Evidence from spinalized mice indicates that motor learning is more effective with AAN than with a fixed trajectory paradigm. In addition, therapist-assisted treadmill training using an AAN strategy facilitates greater improvements in walking ability in ambulatory stroke survivors as compared to robotic-assisted training using a fixed trajectory paradigm. Thus, applying a controlled load using an AAN strategy encourages the active involvement of the patient to enhance the training efficacy of robotic BWSTT.
For high functioning patients, an assistance only training paradigm may be less effective than no assistance for improving walking ability. Thus, the present system applies an adaptive disturbance load to the paretic leg of ambulatory stroke patients to produce a deviation in step kinematics, thereby improving the efficacy of BWSTT. This is supported by results from arm training in patients post stroke. Specifically, data from hemiparetic subjects practicing upper limb movements with forces that provide passive guidance vs. error enhancement indicate that greater improvements in performance are achieved when errors are magnified. These results indicate that causing adaptation by using error-augmentation training might be an effective way to promote functional motor recovery for patients with stroke.
In addition, results from locomotor training in healthy subjects show that motor learning is accelerated by amplifying, rather than reducing, movement errors. Thus, applying a tolerated disturbance load to produce kinematic deviations of the leg during treadmill training may accelerate the motor learning during BWSTT in the patient following a stroke or spinal cord injury.
Motor adaptations driven by disturbance loading may produce ‘aftereffects’ that improve stepping performance and eventually enhance training paradigms. In animal preparations, locomotor behavior can be conditioned to overcome an obstacle and the animal continues to step with an elevated trajectory on the removal of the obstacle. This aftereffect suggests a remodeling of locomotor patterns in anticipation of the perturbation. There is similar evidence from human experiments showing lasting modifications in response to sustained alterations in walking conditions. Human infants and adult subjects adapt to the constant presence of a disturbance to swing phase movements and show aftereffects upon removal of the disturbance.
There is also evidence for modifications in interlimb coordination after a period of walking on a rotating disk or a split-belt treadmill. The presence of aftereffects after a period of training with a disturbance implies the formation or recalibration of the motor output for a given task, suggesting that adaptive training might also prove useful during gait rehabilitation. It is likely that these motor adaptation mechanisms are driven by kinematic deviations from a normal walking pattern, such that disturbances to the leg during stepping can be used to increase the drive to the leg through a motor adaptation mechanism. These motor adaptations, which occur relatively rapidly, are likely to engage neural pathways useful for enhancing longer-term (weeks) training. A durable long-term adaptation may be a consequence of repeated exposures to rapid short-term plasticity associated with a given dose of training.